According to recent developments of computers and peripheral equipments, platemaking methods of lithographic printing plates using various digital printers have been proposed. As such platemaking methods of lithographic printing plates, for example, platemaking methods using a xerographic laser printer for platemaking as described in JP-A-6-138719 and JP-A-6-250424, platemaking methods using on-demand ink-jet printer with thermofusible ink for platemaking as described in JP-A-9-58144, or platemaking methods using thermal printer with thermal transfer ink ribbon for platemaking as described in JP-A-63-166590, or the like, are known.
The platemaking methods using various digital printers as mentioned above have benefits capable of platemaking lithographic printing plate simply and easily because of requiring no limitation on safe light in handling and requiring no development treatment with a developer after image recording, unlike conventionally known platemaking methods of lithographic printing plates having a silver halide emulsion layer or platemaking methods of lithographic printing plates having a water retention layer surface coated with photosensitive resin. The printing plates used for platemaking system using digital printers are correctively referred to as a “processless printing plate”.
However, all of the processless printing plates have problems as mentioned below, since a printing plate is formed by transferring an oil-sensitive (or lithographic printing ink-receivable) recording image to a support surface on which a water retention layer is provided.
1) Since the image forming layer is hydrophlic, the attachment of toner, ink and the like is insufficient. As a result, there are problems such as lack of transferred toner image density, and appearance of white spots in the transferred image.
2) Since the fixed status of the transferred image is insufficient, printing wear resistance is insufficient. As a result, there are problems such as loss of a part of small point character, small points in dotted image, in particular.
3) Due to that a small amount of toner is irregularly transferred to nonimage area, and thermal transfer ink ribbon is rubbed, there are problems such as occurrence of light scumming in whole.
As a method of obtaining lipophilic image area by providing an image-forming layer containing thermoplastic resin on a support without providing water retention layer on the support, and carrying out heat printing, known are a method of obtaining lipophilic image area by directly conducting thermal lithography with thermal head etc. without via thermal transfer ribbon to the image-forming layer, or a method of obtaining lipophilic image area by conducting thermal lithography with infrared laser etc.
As a direct heat-sensitive lithographic printing plate used for platemaking method in which thermal lithography is directly conducted using thermal head etc without via direct thermal transfer ribbon etc, known is a direct heat-sensitive lithographic printing plate having an image-forming layer containing water-soluble polymer compound and a thermofusible material as described in JP-A-58-199153 (Patent Literature 1), or JP-A-59-174395 (Patent Literature 2), or the like. On the other hand, as a heat-sensitive lithographic printing plate used for a method of obtaining lipophilic image area by thermal lithography with infrared laser etc, known is a heat-sensitive lithographic printing plate having an image-forming layer containing thermofusible particulars or thermoplastic polymer as described in JP-A-2000-190649 (Patent Literature 3), JP-A-2000-301846, (Patent Literature 4) and the like.
However, in general, such a heat-sensitive lithographic printing plate and a direct heat-sensitive lithographic printing plate have problems such as difficulty in obtaining clear printed image, insufficiency of printing wear resistance and a higher rate of occurrence of scumming since difference in hydrophlicity/lipophilicity between nonimage area and image area is insufficient. Besides, the direct heat-sensitive lithographic printing plates as described in Patent Literature 1, Patent Literature 2 and the like above have, in addition to the problems above, problems such as a higher rate of occurrence of so-called sticking phenomenon, that is, a phenomenon that thermofusible materials are cooled and fixed to thermal head during thermal lithography, since the printing plates are directly subject to thermal lithography using thermal head etc.
As a heat-sensitive lithographic printing plate capable of providing high image density, known is a heat-sensitive lithographic printing plate having an image-forming layer containing an inorganic pigment, a thermoplastic resin and a thermofusible material as described in JP-A-63-64747 (Patent Literature 5). Besides, in the above-mentioned Patent Literature 3 and Patent Literature 4, as a means for improving balance between lipophilicity of image area and hydrophlicity of nonimage area, a method of coating thermofusible fine particulars which exhibit lipophilicity with a material having specific thermal conductivity, and an idea of hydrophobizing hydrophilic group in hydrophlic polymer by utilizing chelate reaction with heat, are disclosed. However, based on the reasons that any of the reactions are hard to control, and difference in hydrophlicity/lipophilicity between nonimage area and image area is insufficient, they have problems such as difficulty in obtaining clear printed image, insufficient printing wear resistance and a higher rate of occurrence of scumming.
On the other hand, JP-A-6-270572 (Patent Literature 6) and JP-A-7-25175 (Patent Literature 7) disclose a direct heat-sensitive lithographic printing plate by which the generation of sticking phenomenon has been reduced by introducing thermoplastic materials which generates hydroxyl group by thermal decomposition. However, both printing plates have insufficient difference in lipophilicity of image area and hydrophlicity of nonimage area.
[Patent Literature 1] JP-A-58-199153
[Patent Literature 2] JP-A-59-174395
[Patent Literature 3] JP-A-2000-190649
[Patent Literature 4] JP-A-2000-301846
[Patent Literature 5] JP-A-63-64747
[Patent Literature 6] JP-A-6-270572
[Patent Literature 7] JP-A-7-25175